The present invention relates to curable, substantially solvent-free materials, particularly prepolymer curing systems in combination with a bituminous material. More specifically, the present invention is directed to the use of a compatibilizer to disperse the bituminous material into a liquid prepolymer system so as to form a stable dispersion, without using a solvent such as an aliphatic or aromatic liquid commonly used to dissolve asphalt and form a miscible blend with the liquid prepolymer. The goal was to form a solvent-free, stable dispersion of the bituminous material in the prepolymer which upon being cured, preferably at ambient conditions, would result in an adhesive elastomer useful as a coating, adhesive, sealant, caulk, or similar material.
By "bituminous material" is meant bitumen or asphalt. Tars and pitches are not covered by the present invention. Tars are obtained from the thermal decomposition of natural organic substances. Pitches are the residue of tar distillation. Bitumens are complex mixtures comprising polycyclic hydrocarbons and oxygen-containing acyclic and heterocyclic compounds. Bitumens are the dark, solid or semi-solid, high molecular weight hydrocarbons obtained from processing crude oil and the natural asphalt fraction soluble in carbon disulfide. Asphalt is a dark, cementitious material having a solid or semi-solid consistency, which occurs naturally or as a petroleum derivative. Asphalts are generally mixtures of bitumens and mineral substances.
For ease and convenience, since bitumens and asphalts., are both used in the dispersions of this invention, and because of their similar behavior herein, the term "asphalt" will be used hereafter to refer to both asphalts and bitumens.
Because asphalt is inexpensive, has a relatively high penetration value when applied to most porous surfaces, and is relatively weather-resistant and water-impermeable, it has traditionally been used as a main component of protective films, adhesives, binders, etc. Asphalt in blends or emulsions, are used in large quantities for a wide array of products used in paving and roofing; for joint sealants, specialty paints, electrical laminates and hot melt adhesives; as diluents in the manufacture of low-grade rubber products, as diluents for the disposal of radioactive waste; for hot-dip coatings, and for water-retention barriers. Many such blends or emulsions are formulated with a curable liquid prepolymer, to be spread at ambient conditions, and to cure after they are spread, into a rubbery mass.
However, the spreadability of such blends generally derives from their being diluted with a volatile solvent, which is a common solvent for the bituminous material as well as for the prepolymer. Such solvents used have been toluene, aromatic oils, naphtha, mineral spirits or carbon disulfide. Though the amount of a solvent used may only provide partial solubility of the asphalt, the effect of the solvent is to suspend the base material forming a dispersion. After mixing, the dispersion can be easily applied by conventional technology so that, after the solvent evaporates, the asphalt is left intermixed with the other constituents.
As long as more than 25 years ago, an effort to avoid using a solvent in a blend of a polyurethane prepolymer and asphalt was disclosed in U.S. Pat. No. 3,179,610 to Wood, but because of the problem of maintaining a stable dispersion he mixed the components and immediately used them to bind an aggregate such as is used in road paving. He then cured and tested the cured aggregate-binder mixture for stability.
The problem of incorporating a bituminous material in a polyurethane prepolymer was solved in a method disclosed in U.S. Pat. No. 4,871,792 to Lucke who used a combination of a primary plasticizer, namely butylurethane-formaldehyde-carbamic acid ester resin, and a secondary plasticizer, namely 1-methyl-2,3-dibenzylbenzene (2,3-dibenzyl toluene), to provide the requisite solubility of the bitumen in the prepolymer. As he states, his goal was to produce a "onecomponent", that is, single phase, system. This solution to the problem is quite different from the one set forth in this specification which teaches producing a stable dispersion of a bituminous material ("asphalt") which is maintained as a separate phase because it is not soluble in the prepolymer phase.
Thus, though there have been numerous attempts to provide a blend of a liquid, preferably ambient-curable prepolymer, with asphalt, the critical importance of maintaining the asphalt as the dispersed phase in a continuous phase of a polyurethane prepolymer was recognized only in my U.S. Pat. No. 5,008,311 but I was unaware of the importance of the size of dispersed asphalt microglobules or microdroplets (hereafter "particles") to maintain stability. Maintaining a stable dispersion of the asphalt particles in the continuous prepolymer phase is made possible by the use of a compatibilizing agent, or "compatibilizer", having long chains of connected carbon atoms, one end of each chain having, at or near its end, at least one OH group, thought to provide hydrogen bonding with repeating units derived from the ether, ester, isocyanate, siloxane, clefin or diolefin repeating units; the other end of each chain having a high affinity for an asphalt particle. The OH group of the compatibilizer may also react with some of the isocyanate groups on the prepolymer chains, though the extent to which this occurs is not known, and if such a reaction does occur, it will enhance the compatibility of the polar portion of the compatibilizer with the prepolymer.